1. Field of the Invention
The present invention relates generally to apparatus for detecting cosmetic defects in transparent components and, more particularly, to automated apparatus for detecting and analyzing scratches, bubbles, chips or other surface or subsurface defects in ophthalmic lenses.
2. Description of the Prior Art
After a surface of an ophthalmic lens has been ground and polished or otherwise provided with the desired finished curvature, it becomes necessary to inspect that surface to ensure that its quality is within acceptable tolerances. Specifically, the lens surface must be examined to ensure that scratches, chips or other cosmetic defects have not been introduced by the manufacturing operation or, at least, to ensure that any defects that are present are not serious enough to necessitate rejection of the lens. At the present time, the most common type of inspection procedure is to employ inspectors to examine the lenses one at a time as they come off the production line. Usually, the inspector merely looks through the lens at various angles with the aid of a bright light in the hope that any defects present will be found. Alternatively, he may project an image of the lens onto a suitable screen such that any defects in the lens will become visible on the screen.
There are several inadequacies with these techniques. For one thing, with human involvement, the determination of whether or not a lens is satisfactory is subjective in nature and, hence, not very precise. Different inspectors can and frequently do have different standards and as a result marginally acceptable lenses may often be unnecessarily rejected resulting in increased costs while poor quality lenses may sometimes be passed resulting in bad publicity to the manufacturer. Another problem with manual inspection is that defects in the lens surface may often be hidden by external surface debris such as fingerprints, dust and the like which can render the examination inaccurate, or, at least, necessitate that the lens be cleaned prior to inspection. Finally, in the manufacture of semifinished ophthalmic lenses wherein only one surface of the lens is completely finished (usually the front surface), discrimination must be made between defects on the finished and unfinished sides, since the tolerance standards are different. This makes the examination process even more difficult.
Automation of the lens inspection process has been suggested in recent times. However, those systems that have been publicized are not able to effectively distinguish between actual defects and mere surface dirt, or between first and second surface defects (in case of semifinished lenses) and thus are only of limited value.